Remove stale files from lib/html/src.

lib/html/src/KeyboardEventWrappingImplementation.dart

-// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-class KeyboardEventWrappingImplementation extends UIEventWrappingImplementation implements KeyboardEvent {
-  KeyboardEventWrappingImplementation._wrap(ptr) : super._wrap(ptr);
-
-  factory KeyboardEventWrappingImplementation(String type, Window view,
-      String keyIdentifier, int keyLocation, [bool canBubble = true,
-      bool cancelable = true, bool ctrlKey = false, bool altKey = false,
-      bool shiftKey = false, bool metaKey = false, bool altGraphKey = false]) {
-    final e = dom.document.createEvent("KeyboardEvent");
-    e.initKeyboardEvent(type, canBubble, cancelable, LevelDom.unwrap(view),
-        keyIdentifier, keyLocation, ctrlKey, altKey, shiftKey, metaKey,
-        altGraphKey);
-    return LevelDom.wrapKeyboardEvent(e);
-  }
-
-  bool get altGraphKey() => _ptr.altGraphKey;
-
-  bool get altKey() => _ptr.altKey;
-
-  bool get ctrlKey() => _ptr.ctrlKey;
-
-  String get keyIdentifier() => _ptr.keyIdentifier;
-
-  int get keyLocation() => _ptr.keyLocation;
-
-  bool get metaKey() => _ptr.metaKey;
-
-  bool get shiftKey() => _ptr.shiftKey;
-
-  bool getModifierState(String keyIdentifierArg) {
-    return _ptr.getModifierState(keyIdentifierArg);
-  }
-}